The switched mode power supply (SMPS) is a well-known type of power converter having a diverse range of applications by virtue of its small size and weight and high efficiency, for example in personal computers and portable electronic devices such as cell phones. A SMPS achieves these advantages by switching one or more switching elements such as power MOSFETs at a high frequency (usually tens to hundreds of kHz), with the frequency or duty cycle of the switching being adjusted by a feedback loop (also widely referred to as a “compensation loop” or “feedback circuit”) to convert an input voltage to a desired output voltage. A SMPS may take the form of a rectifier (AC/DC converter), a DC/DC converter, a frequency changer (AC/AC) or an inverter (DC/AC).
A switched mode power supply typically has at its output banks of capacitors of different kinds that are arranged in a low-pass filter configuration to low-pass filter the output signal of the switching circuitry of the SMPS that includes the switching element(s). Moreover, the different kinds of capacitor generally have different costs, in terms of their price and/or the area they take up on a circuit board (which often needs to be as small as possible), or other design constraints.
As electronic systems become more and more cost- and space-limited, there is an increasing need to optimise the decoupling filter of the switched mode power supplies that power these systems, particularly as the decoupling filter of the SMPS tends to occupy a large proportion of the board space. An optimisation of the configuration of the decoupling filter (in terms of the numbers of capacitors of different kinds, and how these capacitors are arranged throughout the filter structure) can thus save valuable board space as well as cost. However, the requirement for a steady DC voltage, which is common to many modern electronics systems, imposes tough restrictions on the configuration of the decoupling filter, which complicates the task of selecting an optimum configuration of the capacitors therein.
Conventional approaches to designing the decoupling filter have tended to employ an iterative process, by which a filter design is assessed by examining the load transient response of the SMPS of which it forms a part, and modifying the configuration of the filter—essentially by trial and error—for assessment in the next iteration of the process. However, this approach is time-consuming and usually results in a sub-optimal configuration of the decoupling filter.